The purpose of this article is to answer the question of the legal nature of the European clause contained in the Spanish Constitution. The article examines how it has influenced the process of European integration and the constitutional order in that country. This has been done by analysing the provisions of the Spanish Constitution and the jurisprudence of the Constitutional Tribunal using Spanish constitutional law studies. In the author's opinion, the rather general and open European clause, although it required the jurisprudential activity of the Constitutional Tribunal, proved to be quite functional, becoming the basis of the relationship between Spanish law and EU law and remains unchanged to date.